1. Field of the Invention
The invention relates to a pneumatic pressure-reducer, of the type in which a comparison capsule, sensitive to the opposing actions of a compression spring and the pressure prevailing downstream from a control valve, controls the movements of the flap of the valve, by means of a movable pressure reduction control rod.
Such a device may be used in all technical fields requiring pneumatic control, notably when a particularly accurate and stable control is desired and when the presence of micro-particles is undesirable. Among these fields, space applications will be cited in particular, and in no way limitatively.
2. Discussion of the Background
In a pneumatic pressure-reducer, a pressurised gas is reduced to a controlled lower pressure, by means of a valve formed from a flap pressed elastically against a seat. Movements of the flap away from the seat, providing the reduction in pressure of the gas, are controlled by a movable rod, usually mounted sliding in the body of the pressure-reducer. In order to provide the movements of the rod, the latter is connected to a comparison capsule acted on by a compression spring which tends to move the rod in the direction of opening the valve. In order to provide control, the face of the comparison capsule opposite the one acted on by the compression spring is placed in a comparison chamber situated downstream from the valve and through which the gas which escapes from the pressure-reducer usually passes.
In pneumatic pressure-reducers constituted in this way, compression of the spring which acts on the comparison capsule creates unwanted transverse forces, which in their turn cause friction between the control rod for the valve and the bearings which support it. This friction creates random control inaccuracies and forms micro-particles. For this reason, pressure-reducers of this type are not suited to certain specific applications such as space applications developed currently.
Furthermore, as a result of the comparison chamber being placed directly downstream from the valve, oscillations generated by the reduction in pressure of the gases are transmitted in full to the comparison capsule. Under certain flow conditions, this creates regulation instabilities also little suited to certain specific applications.